Physics 1230: Light and ColorIvan I. Smalyukh, Instructor

Office: Gamow Tower, F-521Email:

ivan.smalyukh@colorado.edu

Phone: 303-492-7277

Lectures: Tuesdays & Thursdays,

3:30 PM - 4:45 PMOffice hours:

Mondays & Fridays, 3:30 PM – 4:30 PM

TA: Jhih-An Yang jhihan.yang@colorado.edu 

Class # 14

Chapter #4: Cameras & Photography

2

Equivalent exposure settings (same light)

¼ sec. lets subjects move

Background in focus(good depth of field)

1/250 sec. stops motion

Background out of focus

3

Which f-number gives half the light of f-4?

A. f-2B. f-2.8C. f-4D. f-5.6E. f-8

f = F/D, so you need a LARGER f-number for less light. 5.6 is sqrt(2) smaller than 4, so twice the light.

4

Which pair gives the same amount of light?

1/30 sec. and f number 4 and

a) 1/120 sec. and f-1b) 1/120 sec. and f-2c) 1/120 sec. and f-4

4x more light for ¼ the time.

55

Lec. 9: Ch. 4 –The Camera and Photography\

Camera partsLenses for camerasControlling light

Photography as artPhotography as science

We are

here

5

66

Albert Bierstadt

Looking Down Yosemite ValleyOil painting

1865

77

Ansel Adams

88

William Henry Jackson. Mountain of the Holy Cross. 1873.

Photography replaced paintingto describe the western US

Albert Bierstadt

Looking Down Yosemite ValleyOil painting

1865

99

Wright Bros., 1903

Photography as proof. Jackalope, 2003?

1010

Alfred Stieglitz1864-1946Photography as art

1111

Edward Steichen,1879-1973Glamour photography

12

Edward Weston

1886-1958

Compare to 15th century painting with folded cloth

13

Imogen Cunningham1883-1976

Ansel Adams by Cunningham

14

“Fine focus”

Means directional lighting

“Soft focus” (not out of focus)

Means diffuse lighting

1515Ansel AdamsSnake River 1942

1616

Lec. 12: Ch. 4 –The Camera and Photography

Camera partsLenses for camerasControlling light

Capturing imagesDigital images

We are

here

16

How do we capture and save the image?

Cameras existed for hundreds of years (pinhole and lens versions)

The revolution (early 19th century) was FILM: The method to store and reproduce the

images.

Nowadays, we rarely use films

17

1818

Ansel Adams

Digital Image Storage: The CCD

19

CCD: “Charge Coupled Device”.Electronic device for storing images

Light sensor area

Wires go to computer memory.

Digital Image Storage: The CCD

20

CCD: “Charge Coupled Device”.Electronic device for storing images

Light sensor area

Notice the colors.

RGB colored filters in front of the sensors. The Bayer filter.

Digital Image Storage: The CCD

21

CCD: “Charge Coupled Device”.Electronic device for storing images

Rectangular array of PIXELs

Typical array is several thousand by several thousand.

1000x1000 = 1,000,000Pixels,OR

1 MegaPixel.

For photography of objects at different distances from us we use

• A. Camera with CCD that has at least 5 megapixels;

• B. Small aperture (large f-number);

• C. Large aperture (small f-number);

• D. Short exposure;• E. A, B, C, & D

For photography of moving objects we use

• A. Camera with CCD that has at least 5 megapixels;

• B. Small aperture (large f-number);

• C. Large aperture (small f-number);

• D. Short exposure and larger aperture;

• E. A, B, C, & D

Extra credit questions

• What settings we use for small depth of field?

• What settings we use to make photos late in the evening (not much light)?

• What would you do to make a photo during a very sunny day?

• Explain how the photo on the left was done

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Review:

To help you in your preparation for the exam(since many of you find the problems on lenses and curved mirrors somewhat difficult, we briefly review only this part)

Exam time: Regular class time on Tuesday, Oct 11

http://micro.magnet.fsu.edu/primer/java/mirrors/convex.html

30

Ray Tracing: One method to understand spherical mirrors and lenses.

Example:

(A) Or (B):The image is LEFT or RIGHT of the lens. The image is REAL or VIRTUAL.

This device is the ‘magnifying glass’. The image appears larger than the object.

31

Ray Tracing: One method to understand spherical mirrors and lenses.

Example:

What is the magnification?

SO

SI

SI is the image height

SO is the object height

I

O

SM

S Ray tracing plus a ruler to

measure things and you can determine magnification.

Object distance, image distance, focal length

32

XiXo

F

Magnification formula

S0 = object height

Si = image height

Note the similar triangles.

33Demo: big mama lens and bulb

We do the following: Image on opposite side of lens? XI is positive (otherwise negative)Image on opposite side of axis? SI is negative. (otherwise positive) Object lengths are

ALWAYS POSITIVE.

The lens equation:The land of “One-Over-Everything!”

FXX IO

111F = focal length

XO = object distance

XI = image distance

Usually, F and XO are given. We want to find XI OI XFX

111

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Distant objects: Let Xo be very large, say 1,000,000 meters. Then 1/Xo = 0.000001, which is very small. You can ignore it. Then

FX I

11 For distant objects,

the image is at the focal point(ask a burnt ant)

Demo: find focal length of lenses

35

Exam time: Regular class time on Tuesday, Oct 11

Good luck on the exam!

P.S. At home, go through the Photography guide on the next two slides